Abstract
Increased knee flexion is seen as a primary goal in achieving a better functional outcome following TKR. However, the relationship between passive knee flexion and biomechanical outcome remains unclear. The aim of this study was to compare kinematic outcomes in TKR patients and controls during high flexion activities.
A three dimensional motion analysis system and two force platforms were used to collect kinematic and kinetic data from 40 patients who had undergone total knee replacement at least 12 months previously and 40 controls who were matched to the patients for age and gender. Participants completed the following activities six times: standing from a seated position, squatting, and lunging with each leg leading. Peak knee flexion angles and moments were compared between groups using t-tests and the correlations between passive knee flexion and functional knee flexion were calculated using ‘Pearson's r’.
For both squatting and lunging, peak knee flexion in the TKR group was significantly less than in the control group. There was no difference between the two groups for the sit to stand activity as peak flexion for this activity was primarily determined by the chair height.
Squat: control 124, TKR 91 (p<0.001) Lunge - op. forward: control 100, TKR 81 (p<0.001) Lunge - op. trail: control 106, TKR 84 (p<0.001) Sit to stand: control 87, TKR 85 (p=0.5)
Although there were significant correlations between functional and passive knee flexion in the TKR group for the squatting and lunging activities, the patients used only approximately 70 to 75% of their available flexion during these activities. As anticipated, there was only a weak correlation between passive and functional flexion for the sit to stand activity.
Percentage of passive flexion used: squat: 77%, lunge - op. forward: 68%, lunge - op. trail: 70% Sit to stand: 71%, Correlations: squat: 0.50, lunge - op. forward: 0.57, lunge - op. trail: 0.50, Sit to stand: 0.27
Normal sagittal knee kinematics during high flexion activities was not restored following TKR. Patients did not or were unable to use their available range of flexion to achieve a normal kinematic pattern. The cause of this important functional deficit remains to be established but may be amenable to targeted rehabilitation.
